The fabrication of integrated circuits (IC) in the semiconductor industry typically employs plasma to create and assist surface chemistry within a plasma reactor necessary to remove material from and deposit material to a substrate. Plasma can be formed in numerous sources, including a capacitively coupled plasma (CCP) source, an inductively coupled plasma (ICP) source, an electrostatic radio frequency (ESRF) source, or any combination thereof.
In general, plasma is typically formed under vacuum conditions by heating electrons to energies sufficient to sustain ionizing collisions with a supplied process gas. Moreover, the heated electrons can have energy sufficient to sustain dissociative collisions, and therefore, a specific set of gasses under predetermined conditions (e.g. chamber pressure, gas flow rate, etc.) are chosen to produce a population of charged species and chemically reactive species suitable to the particular process being performed within the chamber (e.g. etching processes where materials are removed from the substrate or deposition where materials are added to the substrate).
Although the formation of a population of charged species (ions, etc.) and chemically reactive species is necessary for performing the function of the plasma processing system (i.e. material etch, material deposition, etc.) at the substrate surface, other component surfaces on the interior of the plasma processing chamber are exposed to the physically and chemically active plasma, and in time, can erode or become coated with deposits. The erosion or coating of exposed components in the plasma processing system can lead to a gradual degradation of the plasma processing performance and ultimately to complete failure of the system. Thus, various parts of a plasma processing system consist of consumable or replaceable components that are fabricated from silicon, quartz, alumina, carbon, or silicon carbide, for example and placed in the processing system to protect more critical components. Examples of consumable system components include electrodes, shields, rings, baffles and liners.
The consumable nature of these components requires that they be periodically cleaned or replaced. However, consumable components are commonly replaced or cleaned only after detrimental processing conditions or process results are observed. The adverse processing conditions can include plasma arcing, particle formation, variations in substrate etch rate, etch selectivity and etch uniformity. Alternatively, consumable components may be replaced or cleaned according to a predetermined maintenance schedule that can, for example, be based on the number of plasma operating hours. However, these methods can result in overdue or premature replacement or cleaning of consumable system components. In view of these inaccuracies, consumable components are frequently inspected, not only to ensure compliance with strict tolerances, but to avoid premature cleaning and replacement of the consumable components.
Conventionally, measurement metrology techniques, such as measuring the consumable component with precision calipers or some other general purpose measuring tool are utilized. However, such techniques typically require stopping the chamber process to gain internal access, and possibly disconnecting and removing the consumable component from their plasma chambers, which can be labor intensive and result in expensive down-time for personnel and plasma processing tools. Moreover, the use of general purpose measuring tools to test a consumable component requires accurate reading of the tool as well as knowledge of the desired dimension for the particular consumable component being measured. These requirements can lead to false indications of the status of the consumable component.
One alternative method of determining the status of a part is by manufacturing the consumable component with a mark such as an etch or scribe mark, the visibility of which aids in determining whether a consumable component is within tolerance. For example, a mark may be formed by scribing a symbol to a particular scribe depth in the part. When the part is subject to processing and cleaning, one can determine whether the part has eroded beyond the scribe depth by simply verifying whether the symbol is visible or not. While this method can allow inspection of the consumable component condition without compromising the process vacuum, this method requires a specially manufactured part having the scribe depth formed therein. Moreover, a consumable component may have different tolerances for different processes performed in the chamber. Therefore, the depth of the scribe mark must be specifically calculated to consider both the consumable component and the chamber processes that the consumable component will be exposed to during use may result in an otherwise generic process part becoming process specific. Still further, consumable components have been equipped with a cavity formed at a certain depth in the consumable component and configured to emit light when exposed to a process environment of the processing system. Thus, when the consumable component is eroded enough, the emitter can emit light to indicate that the consumable component should be replaced. However, these consumable components also typically require specific manufacturing and/or can render a generic part process specific as described above. Moreover, these parts require sophisticated and expensive optical emission spectroscopy systems.